A drug is administered as a continuous intravenous infusion at a constant rate. Approximately how many elimination half-lives are required for plasma concentration to reach 95% of the eventual steady-state value?
- A 1 to 2
- B 2 to 3
- C 4 to 5 ✓
- D 8 to 10
Correct answer: C. 4 to 5
Explanation
During constant-rate infusion, accumulation follows an exponential approach to steady state. After each half-life, the concentration rises by half the remaining gap: 50% after one, 75% after two, 87.5% after three, and about 94% after four half-lives. Five half-lives gives roughly 97%, so 4 to 5 half-lives approximates 95%. The time to steady state depends only on half-life, not on infusion rate; a faster infusion raises the final concentration but does not shorten the time to reach it.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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